This invention relates generally to magnetic circuits and particularly to obtaining flux rate of change (flux rate) information in a magnetic circuit such as may be used for vibration attenuation in a magnetic forcer system. More particularly, this invention relates to a passive arrangement for the purposes described and, as such, features passive circuitry to implement closed loop control of flux rate of change.
Many arrangements have been developed for the attenuation of vibrations in, for example, magnetic forcer systems, or other mechanical devices. These arrangements can be either passive or active. A passive arrangement relies on internally supplied power. An active arrangement, on the other hand, requires an external power input. An active broadband arrangement wherein a broad range of vibration frequencies are attenuated is described and claimed in commonly assigned U.S. Pat. No. 5,329,416, and an active tuned arrangement wherein a narrow range of vibration frequencies are attenuated is described and claimed in commonly assigned U.S. Pat. No. 5,399,290, both of which applications were filed by R. Ushiyama on Jun. 30, 1993.
Passive arrangements include spring/mass devices, mechanical dampers and hybrid visco-elastic devices, and are characterized by energy losses, or impedances such that energy transfer does not occur.
For example, spring/mass devices typically have low energy transfer characteristics above the natural frequency (impedance), whereas mechanical dampers have well defined loss characteristics. Hybrid visco-elastic devices have both of these characteristics. The choice of a suitable passive arrangement depends on a variety of factors peculiar to a particular application. However, mechanical dampers are not practical where dissipative losses can lead to thermal problems, and impedance adjustments are typically acceptable only for implementations where vibration disturbance frequencies are limited in range.
The present arrangement features a passive arrangement having a control loop which is tuned for a range of frequencies within which vibrations are attenuated. This arrangement is particularly applicable for implementation where cost is a factor and the degree of attenuation required is moderate. As such, the present arrangement requires only a secondary coil winding and the selection of appropriate inductance, resistance and capacitance values for a tuned circuit.